Artificial foot



Feb. 1, 1949. E. PVCARMICHIAELIET AL 2,460,446

ARTIFICIALIFOOT Filed Sept". 2:5, 1947 wh m w ,CC md r w 5 mmm fl Ma 5f m Patented Feb. 1, 1949 ARTIFICIAL Foor Edward P. Carmichael, La Mesa, and Charles W.

Radcliffe, Albany, Calif., assignors toConsolidated Vultee Aircraft Corporation, San Diego Calif., a corporation of Delaware Application September 23, 1947, Serial-No. 775,686 17 Claims. (Cl. 3-5) The present invention relates to improvements in artificial limbs and more particularly to a novel construction for an artificial foot.

Conventional artificial feet'are ordinarily constructed of one of three types of material: wood (usually willow), felt or vulcanized rubber. Feet so constructed, though having many desirable features, are yet characterized by their being relatively heavy and costly. "Such conventional materials as are employed require a method of fabrication which does not lend itself readily to mass production but rather there is demanded relatively skilled personnel to effect the desired contour and exterior appearance. A construction for a foot is contemplated by this invention utilizing light-weight materials which renders the finished product light in weight and relatively in-' expansive to manufacture and which foot would adequately meet all the requirements of a satisfactory and dependable foot prosthesis.

V Figure 4 is atop plan view of the artificial toot of the present invention; again forclarity showing the ankle joint assembly-in dotted outline.

lieferring now in detail to the drawings, there is shown illustrated anartificial leg indicated generally at l0, embodying a, shank ll, only the lower portion of. which is illustrated, and a foot prosthesisl2, connected together -for common operation by an ankle joint. assembly 13. .The specific construction "of the shank H vforms no part of the present invention, it being understood that the foot 12 is adapted for. use with any variety of shank to which it may be .connected as by an articulated joint. The shankl l illustrated herein is therefore 'butone form suitable foruse with the foot l2 of the prese'nt'invention. 1 Shank It is therefore an object of this invention toprovide a foot prosthesis of improved construction which is light in weight, has high impact strength and which has the further advantage of durability.

Another object of the invention lies in the provision of a natural appearing foot prosthesis of improved construction utilizing materials in the composition thereof having a high strengthto-weight ratio and which materials are easily worked.

A further objects construction for an artificial foot, the parts whereof are readily fabricated and in sizes. to fit the needs of the individual amputee and which parts are combinedin a manner designed to take resides inproviding a novel full advantage of their desirable characteristics.

A still further object of the invention is the provision of an improved form of artificial foot which has simplicity of construction, is inexpensive to manufacture, and which may be worn by the amputee with. comfort.

Other objects and features of the invention will be readily apparent to those skilled in the art fromthe following specification andappended drawings illustrating certain preferred embodiments of the invention in which:

Figure 1 illustrates a sectional view of an artificial foot constructed in accordance with the present invention;

' Figure 2 is a sectional-view of the foot taken along line II--II of Figure 1 and for clarity and simplicity showing the ankle joint assembly in dottedjoutline only; 1 Figure 3 is a sectional 'view, enlarged, taken along line III-.-III of Figure 1; and

H, as shown, comprises a centrally disposed, weight-bearing, tubular column I; about which is positioned a covering or fairing l6 suitably constructed in simulation of a human leg. The tubularcolumn l4 and the covering or fairing It may be comprised of any suitable light-weight material. 1 4

The foot' prosthesis I2'utilizes balsa wood as the basic material -offwhich the primary'structure of the foot is comprised. By employing balsa wood in the construction of artificial ioot 12 a unit is effected which is'much lighterin weight than conventional artificial feet while, yet possessing suflicient strength and durability for the purposes required of it. Balsa wood alone however does not possess therequisitesurface hardness but it has been found that applyinga covering of a'synthetic thermosettingresin impregnated laminate thereon the resistancepf' the basi c material, balsa wood, to compressive and impact'loads was increased. to the desired point. The resin impregnated laminate preferred for use herein i a fibrous glass cloth impregnated with a modified phenolic resin. Y g

The artificial foot I2 is comprised of two major components,"a forefoot or toe sectionll and a primary, weight bearing section [8. The latter section 1 ['8' comprises a basicstructure or core 20 consisting of three'primary load bearing members or'blo'cks of balsa wood, properly oriented relative to one another for maximum strength. These three primary load bearing members comprise a sole 2| of elongated form, an instep, 22, and .a heel 23, the instep 22 and heel being secured to the fiat topsurface of sole 2 I. A layer 24018 a resin impregnated material, of the .type mentioned hereinbefore, is applied to the top surfaceof sole 2| and. serves to bond the instep 22 and heel -23 thereto. Thislayer Zlincidentalll! 3 adds strength to the assembly. The load to be applied to instep 22 and heel 23 will be applied from shank ll. During rotative movement of shank II, as will be described further, this load will be applied to the upper surfaces 25 and 26 of instepZZ-and-heel 23 respectively which are engageable by a portion of shank l I. It has been found that balsa wood can sustain compression loads in a much greater degree when such loads are applied parallel to the grain, therefore the grain of both the instep 22 and heel 23, as is shown in Figure 1, run in a vertical direction which is indicated by double-headed arrows. of the sole 2| however the g'r'a'in thereofruns' in a horizontal direction, as indicated by a horizon-- shape; and appearance of anormalfoot it is necessary to add to this-coreZH-certain fairings of ap propriate configuration, therefore, at either side of core 2fl,3fairi-n gsZT are applied which extend from the bottomrsurface of the sole 2i to the top In the case surface Iof the instep '22'an'd heel23. Thesefaii ings-Tl'Jarepre-shaped andwhenjoined to core 20 'a normal appearing foot is effected. Fairings 2 are connected to core 2!! through the use of bonding 1'ayersl28 of- :resin impregnated material,

of isimilarcomposition to layer 24,- and by the iii use of reinforcing bolts 3 I;

Thetoe-se'cti'on l1 provided forward of core 20 may be'formedof. one block of balsa wood or may preferably be built'up,-as in' the present invention,

of a core portion 32- towhich are bonded side I 'fairings'33 and 34, which fairings complete the simulation of a 'humaniorefoot. The toe section I! is adapted to move relative to core ill. In order that an easy, graceful and a natural ap- P e gait be ned, the motion of toe sec- 11 naturalappearancein the gait. The toehinge of the present invention here preventthe occurrence ;of this fault. Thepresent toe hinge will withstandthe repeated ileir'ings to which it will be subliectedwithout breaking down and will yet provide the amount of resistance to bending necessary to the-attaining of a natural walk.

'Thehingefforthe'toe section 11 is provided by a'la'yer 35 of sandwich construction comprising sheets of .a resin impregnated material disposed on eachside of a central layer of rubber. The resin'impregnatedmaterial utilized is preferably of the same composition as layers 24 and "28 used in bonding together the various blocks of balsa wood comprising core 20. This layer '35 is adapted to serve asmore than a hinge 'for the toe section .11 as it is preferably of sufiicient length and breadth to-cover the entire bottom of .eiiiect of. adding strength to the sole and toe member's 21 and 'I1 and will prevent possible failure of the balsa wood in horizontal shear. Further the bottom of foot l2 will be better able to withstand sharp impact blows and shock.

In addition to strengthening the bottom of foot i2 provision is made for further strengthening of the foot as a whole by. the utilization of further resin impregnated layers. Thus, over the upper surface of the toe section i! there is fitted a layer 4! which is bonded to and covers the core 32 thereof and the two side fairings 33 and 34 associated therewith. Another layer 42 is applied over the'instep 22, side fairings 27 and heel '23 so that core 26 comprised of these elements is substantially fully encased in a covering having-high strength and resistance to shock and sharp impact blows. The layers 24 and 28 used in the bonding together of fairings 21, instep 22, heel 23, and sole 2L also act as reinforcing members for the foot to add to the overall strengththereof;

To prevent the toe section I? from assuming a reverse bend there is provided a length of cloth 43 made 01 a strongmaterial, preferably nylon, whichibridgesa gap-44, of generally triangular or wedgeshape, located between the forefoot l1 and core 20, as best seen in Figure 1. The length of cloth 43, best illustrated in Figure 4, is applied to the upper surfaces-of the toe section H and instep'22, beingbonded to the-reinforcing layers 41 anddlcarried thereon. With cloth 43 in place itis apparent that the toe I! cannot bend in reverse direction beyond the plane of the sole.

As illustrated in Figure 1- there is disposed within gapM a generally wedge shaped member t'made of -rubber, or a material having similar characteristics, which will determine the amount of clockwise movement of toe section ii. The size ofmember 45 is determined at the time that .a fitting is had by the amputee and his manner of walking noted. By trial the correct size is readilyarrivedat. This wedge member 45 alsoacts bothlas a cushion and as a restoring force for the toe H. With the construction hereinbefore described a toe actionsubstantially similar to that of a normal foot will be attained.

Bolted to the tubular element M at its lower end is a stopmember 46, having a flared out portion, as shown, which member '46 moves with the shank Has it rotates in clockwise and counterclockwise direction, as viewed in Figure I, in the .act of walking. The amount of rotative movement of shank 'H is determinedby, a pair of rubber blocks 4'! and 48 located on either side of an ankle cavity 5! provided in foot l2. The first block' 41 is mounted on the top surface 25 ofinstep 22 and the othe'rblock" 48 is secured to the top surface 48 of heel 23. Block 48 will rarely, if ever, be engaged'by stop member 46, engagement occurring on'ly when the artificial leg accidentally distorts. 'But "block 48 is provided nevertheless to determine the extent of such accidental backward movement so that it not become toolarge and injure the ankle connection between the shankli and the foot 12.

In normal walking theshank l I rotates toward and away from the toe section I! and the block 4'? will be constantly engaged and disengaged by stop member 46, carried'by' shank H, as strides are taken by the amputee. The height of this rubber block "4'! determines .the amount of move- .ment, counterclockwise, that may be had by shank ii relative to foot I 2. The individual requirements of a wearer are readily determined by fittings and a block of suitable height is easily arrived at. A readily removable stud 52 mounts the block 41 to the top of-instep 22 and it i a simple matter to eifect a change in blocks. Block 4'! is made of relatively hard rubber but with sufiicient give to it that itabsorbs and cushions the shock of engagement by stop member it and serves to make the to-and-fro move ment of shank ii an even one. i 5

The ankle cavity 5! provided in foot [2 is formed or defined by the fairings 21," the sole 2i, instep 22 and heel 23. This cavity or well 5| is adapted to receive theangle joint assembly l3. As in the case of the shank I the particular construction of the ankle joint assembly I 3 is not the subject of the present invention and it is to be understood that assembly i3 is to be considered as illustrative of but one form of connector that may be used. The ankle joint assem bly l3 does however constitute the subject matter of an application for patent filed July 26, 1947, Serial No. 763,924, which issued into Patent No. 2,450,728 on October 4, 194.8, in the name of Glenn G. Havens. For the purpose of this invention, then, the ankle joint assembly 13 will be described but briefly. As is shown in the drawings, ankle joint assembly'l3 comprises a tubular connector 6! which fits over the lower end of columnar member M. The tubular connector 63, as best seen in Figures 1 and 2, necks down into an elongated, fiat-sided, depending portion 62, the lower end 63 of which is generally arcuate in configuration. A pair of resilient links or connecting elements 64 and 65 are carried by portion 62 and are disposed one on eachside thereof. These links M and 65 are respectively secured to mounting "plates 66 and 61 which mounting plates are disposed in cavity 5| to efiect the connection of shank H to foot [2.

The cavity 5! is lined with laminates of the same resin impregnated material that comprises out of position by anything but a very extreme force.

As a further protection against sharp impact blows there is provided over the foot l2 a cos: metic covering 12 made of rubber and which is slipped over the foot in the same manner that a stocking is. This covering 12, it is obvious, is not a part of the foot construction and may or may not be employed by the wearer.

For best results the balsa wood utilized in the construction of the various parts of the foot l2 of this invention should be of a heavy grade. The physical properties of balsa wood are linearly dependent on its specific gravity and it has been found that balsa woods having specific gravities of about 0.20 and above are to be preferred in the construction of a foot having the desired strength and durability. It is, of course, understood that certain selectivity must be shown in choosing the balsa wood to be worked. The balsa wood used must be free of checks, cracks-er other irregularities that may be detrimental to physical characteristics and the grain should be parallel to its greatest dimension. Experience in. choosing dis 6 suitable'balsa wood is readily acquired by the workman.

If desired, the balsa wood parts may be strengthened by impregnation thereof with a suitable synthetic thermosetting phenolic resin and thereafter suitably cured in an oven. Shear strength and compression strength are increased by impregnation though at the cost of a slight increase in weight. However, the present in vention is not to be confined to the use of treated or untreated balsa Wood for satisfactory foot prosthesis are obtainable with either.

The foot construction described herein is well adapted to mass production because of its use of standardized components which may be preformed. The various components of a fo0t-the toe, instep, heel, and sole may be sized and contoured in quantities. There will be but minor additional forming operations required after these various parts are assembled and fairings of desired shape applied thereto.

The subject artificial footis very light in weight, durable, able to Withstand shock and ofiers sufficient resistance to moisture. A fabricating technique is involved in the construction which is very unlike conventional techniques and which readily lends itself to mass production with consequent lower unit costs.

While certain preferred embodiments of the invention have been specifically disclosed, it is ,un-derstood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

We claim:

1. An artificial foot comprising a primary Weight bearing portion and a toe portion, said primary weight bearing portion comprising an elongated core section and a fairing element applied at each elongated side of said core section, said fairings simulating contours of the human foot, said core section and said fairing elements being comprised of balsa wood, and a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings.

2. An artificial foot comprising a primary weight bearing portion and a toe portion, said primary weight bearing portion comprising a core section formed of a plurality of blocks of balsa wood with the blocks so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood, and a fairing element applied at each side of .said core section, said fairings simulating contours of the human foot, and a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings.

3. An artificial foot comprising a primary weight bearing portion and a toe portion movably connected thereto, said primary weight bearing portion comprising a core section formed of a plurality of blocks of balsa wood with the blocks so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood, and a fairing element applied at each side of said core section, said fairings simulating contours of thehuman foot, said toe portion and said fairings also comprising balsa wood, a protective coating formedof a shock resisting material disposed upon the exterior of the assembled core and fairingsand said fairing elements being comprised of balsa wood, and a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings.

.5. An artificial foot comprising a primary weight bearing portion and a toe portion movably attached thereto, said primary weight bearing portion comprising an elongated core section formed of an instep section, a heel section and a sole section, all suitably joined together, and a fairing element applied at each elongated side. of said core section, said fairings simulating contours of the human foot, said core section, fairing elements and said toe portion being coinprised of balsa wood, a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings, and a similar protective coating encasing said toe portion.

6. An artificial foot comprising a primary weight bearing portion and a toe portion, said primary weight bearing portion comprising an elongated core section formed of an instep section, a heel section and a sole section, all suitably joined. together, and a fairing clement applied at each elongated side of said core section, said fairings simulating contours of the human foot, said core section, fairing elements and said toe portion being comprised of balsa wood, a. fiat hinge member of extended length for rotatively connecting said toe portion to said primary weight bearing portion, said hinge member being secured to the bottom surfaces of both said toe portion and said primary weight bearing portion and serving to strengthen the same to prevent failure in horizontal shear, a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings, and a similar protective coating encasing said toe portion.

'1. An artificial foot comprising a primary weight bearing portion and a toe portion movably connected thereto, said primary weight bearing portion comprising a core section having as components, an instep section, a heel section and a sole section each formed of balsa wood and so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood comprising the various sections, and a fairing element applied at each side of said core section, said iairings simulating contours of the human foot, said toe portion and said fairing elements being also comprised of balsa wood, a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings, and a similar protective coating encasing said toe portion.

8. An artificial foot comprising a primary weight bearing portion and a toe portion movably connected thereto, said primary weight bearing portion comprising a core section and a fairing element applied at each side of said core section, said fairings simulating contours of the human foot, said toe portion comprising a central core and a fairing secured to each side therei 8 of, said primary'weightibearing portion and said toe portion being comprised of; balsa wood, a pro-. tective coating formed of a shock resisting ma terial disposed uponv the exterior of said weight bearing portion; and a similar protective coating encasing said toe portion.

9. An artificial foot comprising a primary weight bearing portion and a toe portion having a movable connection therewith, said primary weight bearingQportion comprising a core section formed'ofi a plurality ofblocks of balsa wood with the blocks so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood, and a fairing element of balsa .wood applied at each side of said core section, said fairings simulating contours of the human foot, said toe portion comprising a central core and a, fairing secured to each side thereof, with said central core and fairings being comprised of balsa wood, and a protective coating formed of a shock resisting material disposed upon the exterior of said weight bearing portion, and a similar protective coating encasing said toe portion.

10. An artificial foot comprising a primary weight bearing portion and a toe portion having a movable connection therewith, said primary weight bearing portion comprising a core section having as components, an instep section, a heel section and a sole section, each formed of balsa wood and soarranged with respect to one another that the principal applied loads will be parallel to the. grain of the wood comprising the various sections, and a fairing element of balsa wood applied at each side of said core section, said iairings simulating contours of the human foot, said toe portion comprising a central, core and a fairing secured to each side thereof, with said central core and fairings being comprised of balsa wood, a protective coating formed of a shock resisting material disposed upon the eX- terior of said weight bearing portion, and a similar protective coating encasing said toe portion.

11. An artificial foot comprising a primary weight bearing portion and .a toe portion, said primary weight bearingportion comprising a core section formed of a plurality of blocks of balsa wood with the blocks so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood, and a fairing element of balsa Wood applied at each side of said core section, said fairing elements simulating contours of the human foot, layers of a strength providing material disposed between said fairings and between said various blocks .of balsa wood where they engage one another, said layers serving also to bond said fairings to said core, and to bond said blocks to one another at their engaging portions, and a protective coating formed of a shock resisting material disposed upon theexterior of said weight bearing portion.

12. An artificial foot comprising a primary weight bearing portion and a toe portion having a, movable connection therewith, said primary weight bearing portion comprising a core section having as components, an instep section, a heel section and a sole section, each formed of balsa wood and so arranged with respect to one another'that theprincipal applied loads Will be parallel to the grain of the wood comprising the various sections, and a fairing element oi balsa wood applied at each side of said core section, layers of strength providing material disposed 9 between said fairings and said core and between said instep and heel sections and said sole section, which layers serve to bond said fairings to said core, and to bond said instep and said heel sections to said sole section, said toe portion comprising a central core and a fairing secured to each side thereof, with said central core and fairings being comprised of balsa wood, layers of strength providing material disposed between said fairings and said central core, said layers serving to bond said fairings to said central core, a protective coating formed of strength providing material disposed upon the exterior of said weight bearing portion to effect a shock resisting covering therefor, and a similar protective coating encasing said toe portion.

13. An artificial foot adapted to be operatively connected to an artificial shank, and comprising a primary weight bearing portion and a toe portion, said primary weight bearing portion comprising a core section having as components, an instep section, a heel section and a sole section, each formed of balsa wood and so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood comprising the various sections, and a fairing element of balsa wood applied at each side of said core sections, said fairing elements simulating contours of the human foot, said instep section, said heel section and said side fairings being arranged relative to one another and cooperating with one another to provide four walls which define a cavity in said primary weight bearing portion, which cavity is adapted to receive means for connecting said artificial foot to an artificial shank, and a protective coating formed of a shock resisting material disposed upon the exterior of said weight bearing portion.

14. An artificial foot comprising a primary weight bearing portion and a toe portion, said primary weight bearing portion comprising an elongated core section and a fairing element ap plied at each elongated side of said core section,

said fairings simulatingcontours of the human foot, said core section and said fairing elements being comprised of balsa wood, means for rotatively connecting said toe portion to said primary weight bearing portion, means for determining the amount of movement of said toe portion relative to said primary weight bearing portion, and a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings.

15. An artificial foot comprising a primary weight bearing portion and a toe portion, said primary weight bearing portion comprising a core section formed of a plurality of blocks of balsa wood with the blocks so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood, and a fairing element applied at each side of said core sections, said fairings simulating contours of the human foot, means for rotatively connecting said toe portion to said primary weight bearing portion, stop means for determining the amount of rotative movement of said toe portion toward said primary weight bearing portion, and a restraining means for determining the amount of rotative movement of said toe portion in the opposite direction, a protective coating formed of a shock resisting material disposed upon the exterior of the assembled core and fairings, and a similar protective coating encasing said toe portion.

16. An artificial foot comprising a primary weight bearing portion and a toe portion having a movable connection therewith, said primary weight bearing portion comprising a core section having as components, an instep section, a heel section and a sole section, each formed of balsa wood and so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood comprising the various sections, and a fairing element of balsa wood applied at each side of said core section, said fairing elements simulating contours of the human foot, said toe portion comprising a central core and a fairing secured to each side thereof, with said central core and fairings being comprised of balsa wood, means for rotativel connecting said toe portion to said primary weight bearing portion, stop means for determining the amount of rotative movement of said toe portion toward said primary weight bearing portion, and a restraining means for determining the amount of rotative movement of said toe portion in the opposite direction, a protective coating formed of a shock resisting material disposed upon the exterior of said weight .bearing'portion, and a similar protective coating encasing said toe portion.

17. An artificial foot comprising a primary weight bearing portion and a toe portion, said primary weight bearing portion comprising a core section having as components, an instep section, a heel section and a sole section, each formed of balsa wood and so arranged with respect to one another that the principal applied loads will be parallel to the grain of the wood comprising the various sections, and a fairing element of balsa wood applied at each side of said core section, said fairing elements simulating contours of the human foot, layers of strength providing material disposed between said fairings and said core and between said instep and said heel sectionsand said sole section, which layers serve to bond said fairings to said core, and to bond said instep and said heel sections to said sole section, said toe portion comprising a central core and a fairing secured to each side thereof, with said central core and fairings being comprised of balsa wood, layers of strength providing material disposed between said fairings and said central core, said layers serving to bond said fairings to said central core, means for rotatively connecting said toe portion to said @primary weight bearing portion, stop means for determining the amount of rotative movement of said toe portion toward said primary weight bearing portion, and a restraining means for determining the amount of rotative movement of said toe portion in the opposite direction, a protective coating formed of strength providing material disposed upon the exterior of said'weight bearing portion to effect a shock resisting covering therefor, and a similar protective coating encasing said toe portion.

EDWARD P. CARMICHAEL. CHARLES W. RADCLIFFE.

REFERENCES CITED The following references are of record in the filo of this patent:

UNITED STATES PATENTS Number Name Date 1,190,915 Kull July 11, 1916 2,170,580 Steele Aug. 22, 1939 

